This invention relates to a chelated mineral composition containing 1,2-disubstituted aromatic ligands. More particularly, this invention relates to mineral chelates containing 1,2-disubstituted aromatic ligands and particularly 2-alkoxyphenol ligands, such as vanillin, and metals selected from the group consisting of Mg, Ca, Cr, Mn, Fe, Co, Cu, Zn, Se, and Mo wherein the ligand to metal ratio is 1:1 to 3:1, preferably 2:1.
When a metal combines with an electron donor, a complex or coordination compound is formed. When the electron donor, also referred to as a ligand or chelating agent, contains two or more donor groups tied together in some way, the resulting complex is a chelate. The essential and characteristic feature found in all chelates is formation of a ring between the ligand and the metal atom. For ring formation to occur, the electron donor molecule must contain two or more groups that can each combine with the metal atom with formation of at least one coordinate covalent bond. Also, groups or atoms (such as oxygen, nitrogen, hydroxyl, and amino) must be present that can coordinate with the metal atom through their lone electron pair. Further, these donor groups must be separated from each other by chains of suitable length to permit formation of rings with five or six member rings being most stable. Albert E. Frost, Fundamental Aspects of Chelation, The Science Counselor (June, 1956).
Amino acids comprise a group of ligands that have been used to chelate minerals. It is known that amino acid chelates form a stable product having one or more five-member rings formed by reaction between the carboxyl oxygen and the .alpha.-amino group of an a-amino acid with the metal ion. Such a five-member ring is defined by the metal atom, the carboxyl oxygen, the carbonyl carbon, the a-carbon, and the .alpha.-amino nitrogen and is generally represented by Formula I. However, the actual structure will depend upon the ligand to metal mole ratio. The ligand to metal mole ratio is at least 1:1 and is preferably 2:1, but in certain instances may be 3:1 or even 4:1 or higher. Most typically, an amino acid chelate may be represented at a ligand to metal ratio of 2:1 according to Formula I: ##STR1##
In the above formula, when R is H, the amino acid is glycine, the simplest of the .alpha.-amino acids. However, R could represent any of the side chains of the other twenty or so naturally occurring amino acids derived from proteins. These .alpha.-amino acids all have the same configuration for the positioning of the carboxyl oxygen and the .alpha.-amino nitrogen. In other words, the chelate ring is defined by the same atoms in each instance. The American Association of Feed Control Officials (AAFCO) have also issued a definition for an amino acid chelate. It is officially defined as the product resulting from the reaction of a metal ion from a soluble metal salt with amino acids with a mole ratio of one mole of metal to one to three (preferably two) moles of amino acids to form coordinate covalent bonds. The average weight of the hydrolyzed amino acids must be approximately 150 and the resulting molecular weight of the chelate must not exceed 800. The products are identified by the specific metal forming the chelate, i.e. iron amino acid chelate, copper amino acid chelate, etc.
Amino acid chelates can also be formed using peptide ligands instead of single amino acids. These will usually be in the form of dipeptides or tripeptides because larger ligands would have a molecular weight which would be too great for direct assimilation of the chelate formed. Generally, peptide ligands will be derived by the hydrolysis of protein. However, peptides prepared by conventional synthetic techniques or genetic engineering can also be used. When a ligand is a di- or tripeptide, a radical of the formula [C(O)CHRNH].sub.e H will replace one of the hydrogens attached to the nitrogen atom in Formula I. R, as defined in Formula I, can be H, or the side chain of any other naturally occurring amino acid and e can be an integer of 1 or 2. When e is 1 the ligand will be a dipeptide and when e is 2 the ligand will be a tripeptide.
The structure, chemistry, and bioavailability of amino acid chelates is well documented in the literature, e.g. Ashmead et al., Chelated Mineral Nutrition, (1982), Chas. Co Thomas Publishers, Springfield, Ill.; Ashmead et al., Intestinal Absorption of Metal Ions, (1985), Chas. C. Thomas Publishers, Springfield, Ill.; Ashmead et al., Foliar Feeding of Plants with Amino Acid Chelates, (1986), Noyes Publications, Park Ridge, N.J.; as well as in U.S. Pat. Nos. 4,020,158; 4,167,564; 4,216,143; 4,216,144; 4,599,152; 4,774,089; 4,830,716; 4,863,898 and others. Flavored effervescent mixtures of vitamins and amino acid chelates for administration to humans in the form of a beverage are disclosed in U.S. Pat. No. 4,725,427.
In the field of mineral nutrition, amino acid chelates have increasingly been recognized as providing certain advantages over inorganic mineral salts. One advantage is attributed to the fact that these chelates are readily absorbed in the gut and mucosal cells by means of active transport as though they were small peptides. In other words, the minerals are absorbed along with the amino acids as a single unit utilizing the amino acids as carrier molecules. Since this method of absorption does not involve the absorption sites for free metal ions, the problems of competition of ions for active sites and suppression of one nutritive mineral element by another are avoided. Other advantages of amino acid chelates include stimulation of gonadotropic hormones, U.S. Pat. No. 4,774,089; delivery of metal ions to targeted tissue sites, U.S. Pat. No. 4,863,898; and enhancement of the immune system, U.S. Pat. No. 5,162,369.
Despite these advantages, use of amino acid chelates for human consumption has the drawback of a metallic aftertaste that some people find disagreeable. Thus, amino acid chelates have had to be taken in capsules and other forms that avoid the aftertaste. Use of amino acid chelates in nutritional beverages has also been limited by this aftertaste.
In view of the foregoing, it will be appreciated that mineral chelates that do not contain amino acids or an unpleasant aftertaste, yet provide the advantage of increased absorption of minerals compared to inorganic minerals, would be a significant advancement in the art.